In recent years, non-contact IC card techniques are used in various aspects of daily life, such as prepaid cards and public transportation tickets.
FIGS. 18(a) and 18(b) schematically show a non-contact IC card and a card reader. As shown in the drawing, when the user holds a non-contact IC card 50 over a card reader 60, a magnetic field A is generated from the card reader 60 to the non-contact IC card 50. This magnetic field A is converted to an electric current when passing through a coil built in the non-contact IC card 50, and used as power for an IC. A magnetic field B whose direction is opposite to that of the magnetic field generated from the card reader 60 is then generated in the non-contact IC card 50, and the response B to the card reader 60 is performed. In this way, the card reader 60 can read information recorded on the non-contact IC card 50.
Thus, the non-contact IC card is convenient because the communication with the card reader is possible simply by holding the non-contact IC card over the card reader. On the other hand, however, since the recorded information can be read without contact, there is also a danger that unauthorized reading called skimming is performed without the bearer's knowledge to thereby have the information stolen.
In view of such circumstances, various attempts are made to prevent non-contact IC card skimming. For example, the inventor previously developed a card having a non-contact IC card skimming prevention function as described in the patent document 1. This card utilizes conductor properties, as shown in FIGS. 19(a) and 19(b). In detail, upon receiving the magnetic field A from the card reader 60, an eddy current is generated in a conductor 10 and a diamagnetic field that cancels out the magnetic field A from the card reader 60 is generated, as a result of which no response is performed from the non-contact IC card 50 to the card reader 60. Hence, the information recorded on the non-contact IC card cannot be read, so that skimming can be prevented.
Moreover, the patent document 2 describes an invention relating to a structure for preventing skimming of a card that carries an information recording medium such as a non-contact IC medium. The invention described in the patent document 2 is configured by laminating a plurality of members such as a fixed shielding member, a spacer member, a movable shielding member, and a laminate member, and includes a shielding unit and a read permission unit. In this invention, the movable shielding member is formed using a material that has a property of shielding, absorbing, or interfering with a communication wave such as an electric wave. Moving the movable shield member makes it possible to switch between a readable state and a non-readable state, and skimming can be prevented in the non-readable state.
Furthermore, the patent document 3 describes an invention relating to an unauthorized access prevention apparatus and an IC card holder that can protect card information from unauthorized access, by putting an IC card in a communicable state only when the card bearer wants to access and otherwise putting the IC card in a non-communicable state.
The invention described in the patent document 3 is configured by selectively short-circuiting or opening a conductive winding that is spirally wound in a plane. In the case where an IC card is placed so as to face the winding, when the winding is in a short-circuit state, an antenna portion of the IC card and the winding are magnetically coupled to each other, and a deviation occurs in antenna resonant frequency of the IC card. This inhibits IC card communication, so that unauthorized reading of recorded information is prevented. When the winding is in an open state, transmission/reception of card information is performed.
[Patent Document 1] Japanese Patent No. 3836496
[Patent Document 2] Japanese Patent Application Laid-Open No. 2007-199888
[Patent Document 3] Japanese Patent Application Laid-Open No. 2004-348500